Normalize quotes
Replace all typographic quote characters with straight ASCII quotes.
Anagram Groups by Size
Group a list of words into anagram groups and return them sorted by group size and lexicographically.
Graph DFS
Return all nodes reachable from a start node via DFS.
Topological sort (Kahn)
Return a valid topological ordering of tasks, or [] if a cycle exists.
Word ladder length
Return the length of the shortest transformation from beginWord to endWord changing one letter at a time.
Employee Hierarchy
Build an employee hierarchy tree and compute the total number of direct and indirect reports for each employee.
Redundant Connection
Given a list of edges forming a tree plus one extra edge, return the edge that appears last in the input and creates a cycle.
Reconstruct Itinerary
Given a list of airline tickets, reconstruct the itinerary in order using each ticket exactly once, choosing the lexicographically smallest path when multiple options exist.
Eulerian Path Check
Given the number of vertices and an edge list of an undirected graph, decide if it has an Eulerian path.
Employees earning more than manager
Given employee records with manager IDs, find those who earn more than their direct manager.
Accounts Merge
Given a list of accounts, merge those that share any email and return sorted accounts.
Graph DFS Generator
Implement a generator function that performs a depth-first traversal of a graph without recursion.
Dijkstra Shortest Path
Implement Dijkstra's algorithm on a weighted graph to return distances from a source to every node.
Bellman-Ford Algorithm
Implement the Bellman-Ford algorithm to compute shortest distances from a source in a directed weighted graph with up to 100 vertices and negative edges.
Cycle Detection in a Directed Graph
Use DFS with a recursion stack to detect cycles in a directed graph.
Cycle Detection in Undirected Graph
Write a function that detects if an undirected graph contains a cycle.
Articulation Points
Implement a function that returns the articulation points of an undirected graph.
Bridges in Graph
Implement a function that returns all bridges in an undirected graph.
Hamiltonian Path Check
Implement a function that checks whether an undirected graph has a Hamiltonian path using DFS and backtracking.
Minimum Cut
Given an undirected graph in adjacency-list form, return the size of the minimum edge cut that disconnects the graph.
Bipartite Graph Check
Implement a function to check if an undirected graph is bipartite using graph coloring.
Graph Coloring
Given an undirected graph, determine if it can be colored with two colors such that adjacent vertices have different colors.
Course Schedule Can Finish
Given numCourses and prerequisites, return whether all courses can be finished without cyclic dependencies.
Alien Dictionary Order
Given a sorted list of words in an alien language, derive the order of its unique letters.
Showing 1–24 of 53 challenges
Guide: free Python coding challenges
Practice Python by solving problems
PythonSkillset challenges are hands-on coding exercises from beginner to advanced. Open a challenge, read the problem, write Python in the split-pane editor, and run tests with Pyodide — no install required.
How to use the arena
- Pick a category — basics, algorithms, strings, and more
- Open a challenge, read the statement, and edit the starter code
- Run tests, fix failures, then try a related quiz or tutorial lesson
Challenges vs tutorials and quizzes
Challenges test what you can build under constraints. For guided teaching, use our Python tutorials. For quick checks, try quizzes or copy snippets from code samples.